Synthesis and characterization of Gd2O3: Er3+, Yb3+doped with Mg2+, Li+ions-effect on the photoluminescence and biological applications

Gd₂O₃:1% Er³⁺, 18% Yb³⁺,x% Mg²⁺(x = 0; 2.5; 4; 5; 6; 8;10; 20; 25; 50) and Gd₂O₃:1% Er³⁺, 18% Yb³⁺, 2,5% Mg²⁺,y% Li⁺(y = 0.5-2.5) nanoparticles were synthesized by homogenous precipitation method and calcined at 900 °C for 3 h in air atmosphere. Powder x-ray diffraction, scanning electron microscopy, cathodoluminescence, transmission electron microscopy, energy dispersive x-ray spectroscopy and photoluminescence techniques were employed to characterize the obtained nanoparticles. We observed a 8-fold increase in red luminescence for samples suspended in DMSO solution for 2.5% of Mg²⁺doping. The x-ray analysis shows that for the concentration of 2.5% Mg, the size of the crystallites in the NPs is the largest, which is mainly responsible for the increase in the intensity of the upconversion luminescence. But the addition of Li⁺ions did not improve the luminescence of the upconversion due to decreasing of crystallites size of the NPs. Synthesized nanomaterials with very effective upconverting luminescence, can act as luminescent markers inin vivoimaging. The cytotoxicity of the nanoparticles was evaluated on the 4T1 cell line for the first time.

Enhanced up-conversion emission in Er3+-doped barium–natrium–yttrium–fluoride phosphors by alkali ion introduction under 1550 nm excitation

This figure shows the emission spectra of nanocrystals with different Li+ ion introducing concentrations at 1550 nm. Compared with the untreated samples, when the Li+ ion introducing concentration is 0.2 mol%, the luminescence intensity of the sample is improved obviously.

Excitation of erbium-doped nanoparticles in 1550-nm wavelength region for deep tissue imaging with reduced degradation of spatial resolution

Rare-earth-doped nanoparticles are one of the emerging probes for bioimaging due to their visible-to-near-infrared (NIR) upconversion emission via sequential single-photon absorption at NIR wavelengths. The NIR-excited upconversion property and high photostability make this probe appealing for deep tissue imaging. So far, upconversion nanoparticles include ytterbium ions (Yb3  +  ) codoped with other rare earth ions, such as erbium (Er3  +  ) and thulium (Tm3  +  ). In these types of upconversion nanoparticles, through energy transfer from Yb3  +   excited with continuous wave light at a wavelength of 980 nm, upconversion emission of the other rare earth dopants is induced. We have found that the use of the excitation of Er3  +   in the 1550-nm wavelength region allows us to perform deep tissue imaging with reduced degradation of spatial resolution. In this excitation–emission process, three and four photons of 1550-nm light are sequentially absorbed, and Er3  +   emits photons in the 550- and 660-nm wavelength regions. We demonstrate that, compared with the case using 980-nm wavelength excitation, the use of 1550-nm light enables us to moderate degradation of spatial resolution in deep tissue imaging due to the lower light scattering coefficient compared with 980-nm light. We also demonstrate that live cell imaging is feasible with this 1550 nm excitation.

The role of Li+ in the upconversion emission enhancement of (YYbEr)2O3 nanoparticles

The mechanism of upconversion enhancement for Li+-doped materials is still contentious. Attempting to settle the debate, here the upconversion emission enhancement of (Y0.97-xYb0.02Er0.01Lix)2O3, x = 0.000-0.123, nanoparticles is studied. Li+ incorporation in the Y2O3 host lattice is achieved via co-precipitation and solid-state reaction routes. In contrast to numerous reports, elemental analysis reveals that the former method does not afford Li+-bearing nanoparticles. The solid-state reaction route accomplishes an effective Li+ doping, as witnessed by inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy and powder X-ray diffraction showed an increase in nanoparticle size with increasing Li+ concentration. Rietveld refinement of powder X-ray diffraction data shows that the cubic lattice parameter decreases with increasing Li+ content. The emission quantum yield increases tenfold with increasing Li+ content up to x = 0.123, reaching a maximal value of 0.04% at x = 0.031. XPS and infrared spectroscopy show that the carbonate groups increase with increasing Li+ content, thus not supporting the prevailing view that the upconversion luminescence enhancement observed upon Li+ nanoparticle's doping is due to the decrease of the number of quenching carbonate groups present. Rather, the particle size increment and the decrease in the lattice parameter of the host crystals are shown to be the prime sources of quantum yield enhancement.

Optical nanoprobes for biomedical applications: shining a light on upconverting and near-infrared emitting nanoparticles for imaging, thermal sensing, and photodynamic therapy

Shining a light on spectrally converting lanthanide (Ln³⁺)-doped nanoparticles: progress, trends, and challenges in Ln³⁺-nanoprobes for near-infrared bioimaging, nanothermometry, and photodynamic therapy.